Tractor brake system protective valves



Oct. 31, 1961 R. H. GEORGE TRACTOR BRAKE SYSTEM PROTECTIVE VALVES 2Sheets-Sheet 1 Filed Nov., 13, 1958 R. H. GEORGE TRACTOR BRAKE SYSTEMPROTECTIVE VALVES Oct. 31, 1961 2. Sheets-Sheet 2 Filed Nov. 13, 1958ATTORNEY United States Patent 3,006,368 TRACTOR BRAKE SYSTEM PRTECTIVEVALVES Robert H. George, Melrose Park, Pa., assigner to BrakemasterCorporation', Philadelphia, Pa., a corporation of Pennsylvania FiledNov. 13, 1958, Ser. No. 773,645 4 Claims. (Cl. IS7-614.2)

This invention relates to tractor brake system protective valves, andmore particularly to valves suitable for use with the automotive airbrake systems of tractor-trailers.

It is the principal object of the present invention to provide valvesfor use with automotive air brake systems of tractor-trailers which willfunction to protect the brake system of the tractor so that the brakesof the tractor can be applied in the case of breakaway of the trailerfrom the tractor.

It is a further object of the present invention to provide valves foruse with automotive air brake systems of tractor-trailers so that theair for the air brakes is safeguarded against backow through the supplyline to the trailer brake system in the event of a breakaway of thetrailer from the tractor.

It is a further object of the present invention to provide valves foruse with automotive air brake systems of tractor-trailers by which anautomatic and prompt operation of the brakes of the trailer will beeiective upon breakaway of the trailer from the towing vehicle.

It is a further object of the present invention to provide tractor brakesystem protective valves for use in air brake systems of automotivevehicles in which a two position dashboard emergency valve is employedfor emergency application of the trailer brakes and which, upon eitherautomatic or manual operation of the dashboard valve, will be availablefor exercising its protective functions.

It is a further object of the present invention to provide tractor brakesystem protective valves which will prevent back ow of air from thetrailer brake system to the tractor brake system in the event of leakageof the no-bleed-back emergency relay and which will operatesatisfactorily with either the bleed back or the no bleed back type ofemergency relay now considered necessary to meet safety requirements.

It is a further object of the present invention to provide valves foruse in automotive air brake systems which will not be adversely affectedby water, oil, carbon and sludge introduced by the compressor anddistributed during operation throughout the air brake system.

It is a further object of the present invention to provide tractor brakesystem protective valves for use with automotive air brake systems whichwill not be rendered inoperative or caused to leak by reason of thepresence of water, oil, carbon and sludge found in such systems.

It is a further object of the present invention to provide tractor brakesystem protective valves for use with automotive air brake systems whichwill function continuously for long periods of time under the difficultconditions encountered in tractor-trailer operation.

Other objects and advantageous features of the invention will beapparent from the description and claims.

The nature and characteristic features of the invention will be morefully understood from the following description, taken in connectionwith the accompanying drawings forming part thereof, in which:

FIGURE l is a diagrammatic View of an air brake system for automotivevehicles with protective valves in accordance with the present inventionemployed therewith;

FIG. 2 is a vertical longitudinal central sectional view of a tractorbrake system protective valve in accordance Fice with the presentinvention for use in the emergency pressure line to the trailer;

FIG. 3 is a vertical longitudinal central sectional view of a tractorbrake system protective valve in accordance with the invention for usein the service line to the trailer;

FIG. 4 is a transverse vertical sectional view taken approximately onthe line '4--4 of FIG. 2;

FIG. 5 is a transverse vertical sectional View taken approximately onthe line 5 5 of FIG. 3; and

FIG. 6 is a transverse vertical sectional view taken approximately onthe line 6-6 of FIG. 2.

It should of course be understood that the description and drawingsherein are illustrative merely, and that various modifications andchanges can be made in the structure disclosed without departing fromthe spirit of the invention.

Like numerals refer to like parts throughout the several views.

Referring now more particularly to FIG. l of the drawings, an automotiveair brake system of known type for tractor-trailers is diagrammaticallyshown having the protective valves in accordance with the inventionincluded therein.

In the system illustrated in FIG. l, an air compressor 10 is employedwhich serves as a primary source of braking air under pressure and whichhas its delivery side in communication with a wet air tank 11 by meansof a fluid connection 12 with a non-return or check valve 13 interposedtherein.

The Wet air tank 11 is in communication with a dry air tank 14 through afluid connection 15 having a nonreturn or check valve 16 interposedtherein.

The dry air tank 14 has a fluid connection 17 which extends to agovernor 18 for the compressor 10 for regulating the compressoroperation and the uid connection 17 can be provided with an indicatinguid pressure gage `19 for indicating the pressure'n the iluid connection17. The fluid connection 17 has a pressure responsive overload reliefvalve 20 connected thereto.

A branch uid connection 21 extends from the fluid connection 17 to afoot valve 22 in the cab of the tractor for pedal control of theapplication and release of the brakes of both the tractor and thetrailer. The foot valve 22 effects a controlled delivery of pressureuid, dependent upon the extent to which it is depressed; and

has a controlled bleed or exhaust to atmosphere etective for brakerelease.

The branch liuid connection 21 also extends to a hand operated valve 23in the cab of the tractor for variable manual control of the applicationand release of the trailer brakes. The valve 23 is similar in its actionto the `foot valve 2.2 in eiectng a controlled delivery of pressureduid, dependent upon the extent to which it is turned, and has acontrolled bleed or exhaust to atmosphere eiective for brake release.

The branch iluid connection 21 also extends to a two position handoperated emergency valve 24 located on the dashboard for the emergencyapplication of the trailer brakes. The valve 24 in its normal andnonemergency p 3 the foot valve 22 and the hand valve 23 to a doubleacting check valve 29.

The dry tank 14 also has a fluid connection 3l) in communicationtherewith and with a tractor brake system protective valve 31, asillustrated in more detail in FIG. 2. Thevvalve 31 also has a iluidconnection 32 thereto from the dash valve 24.

The dash valve 24 has a fluid connection 33 emending therefrom to atractor brake system protective valve 34, which is illustrated in moredetail in FIG. 3, a fluid connection 35' being provided between thecheck valve 29 and the valve 34.

The valve 34 has a normal service line connected thereto for supplyingand returning air, in the normal service operation of the trailerbrakes, and this service line includes in series relation a iluidconnection 36, a connecting 'nipple 37, a ilexible iluid connection orhose 38, a detachable trailer coupling 39 and a iluid connection 40. Theiluid connection 46 is connected to an emergency relay valve 41 of knowntype, and which may beof the type known as a no bleed-back emergencyrelayV valve, or of the type known as a bleed-back emergency relayvalve.

The emergency relay valve 41 has the main trailer air supply tank 42connected thereto by a iluid connection 43 and has connections 44extending to the diaphragms 45 of brake operating motors for brakeapplying operations on the trailer.

yThe emergency relay valve 41 includes valve mechanism of known typewith various operating positions including trailer air supply tankcharging positions with the air pressure below or above a predeterminedlevel, Y

commonly taken as 70 psi. The relay valve 41 also has` normal operatingpositions which include a release position when there is no air pressurein the brake diaphragm chambers 45, an applying position when the airpressureV is delivered .to or increased in the brake diaphragrn chambers45, a balanced position when the mechanism is balanced for maintaining aconstant pressure in the brake diaphragm chambers 45, and a releasingposition in which the mechanism is releasing or reducing the airpressure in the brake diaphragm charnbers 45.

The emergency relay valve 41 also has an emergency position inY whichthe mechanism automatically delivers the full pressureV available in thetrailer tank 42 to the brake diaphragm chambers 45. This emergency brakeapplication is effected when the pressure in the emergency line dropssuddenly due to uncoupling of the coupling 49 or to trailer breakaway,or by actuation ofthe dash valve 24 to its emergency position.

VThe valve 31 has an emergency service line connected thereto forsupplying air for charging the tank 42 and for controlling the emergencyrelay valve 41, and includes in series relation a Huid connection 46, aconnecting nipple 47, a exible huid connection or hose 48, a detachabletrailer coupling 49 and a fluid connection 50 to the emergency relayvalve 41.

The couplings 39 and 49 are the customary couplings employed forconnecting the brake system of the trailer to the brake system of thetractor.

Referring now more particularly to FIG. 2 of the drawings, the tractorbrake systemprotective valve 31 there shown preferably includes a mainhollow cylindrical housing section 55 having an internal cylindricalbore 56, a longitudinally axially dispo-sed internally threaded Y boss57 .for the connection of the fluid connection 32, with an enlargement58 at the other end which is internally threaded at 59.

The housing section 55 has an internal shoulder 66 at the inner end ofthe internaly threaded portion 59.Y

shoulder 66 and an externally threaded end 67 for engagement in thethreaded portion 59 of the housing section 55.

The second housing section 65' has an internal cylindrical Abore `68longitudinally axially aligned with the bore 56, and has an outwardlyextending boss 69 connected thereto and communicating with the bore 68.The boss '69 is internally threaded as at 70 for the connection of theiluid connection 46 thereto.

The second housing section 65 also has an opposite end shoulder 71 andan externally threaded end 73.

A third housing section 75 is provided having an enlargement 7-6 with aninner end shoulder 77 and with an internally threaded portion 78 forengagement of the threaded portion .73 of the second housing section 65.

The third housing section 75 is provided with an internal longitudinallyaxially disposed cylindrical bore S6, a longitudinally axially disposedintermediate cylindrical bore 81 and a longitudinally axially disposedend bore 82, the bores Si?, 81 and 32 Ibeing longitudinally axiallyaligned with the bores 56 and 68.

The inner terminus of the bore provides a limit shoulder 483 forpurposes to be explained, and the end of the bore 531 at itsintersection with the bore 82 provides a valve seat 84.

The third housing section 7S also has a longitudinally axially disposedinternally threaded boss 85 for the connection of the iluid connection3u.

Within the interior of the second housing section 65, a hollow sleeve 99is provided, which has an internal bore 91 longitudinally coaxiallydisposed with respect to the bore 68 to serve Vas ya guide and has aradially outward-ly extending positioning ilange 92 which is engagedbyuthe shoulder 6% at the end of the housing section 55 and the shoulder66 `at the end of the housing 65 for retaining the same in position whenthe housing sections 55 and 65 are assembled.

VWithin the interior of the second housing section 65 falso, a hollowsleeve 93 is provided having an internal bore 94 longitudinallycoaxially disposed with respect to the bore 91. The sleeve 93 has aradially outwardly extend-ing positioning flange 95 which is engaged bythe end shoulder 71 of the housing section 65 and by the shoulder 77 ofthe 'housing section 75 for retaining the sleeve 93 in position when thehousing sections 65 and 75 are assembled.

A piston i106 is provided having a head 161 slidably mounted within t'ne1bore'56, the head 101 being provided with an end groove 102 for thereception of ay packing 103, such as a U-cup of rubber or the like forpreventing fluid leakage along the bore 56 and with a collecting groove164 for the reception of dirt tending to find its way thereinto duringthe movement of the piston 100.

The piston 166 also includes, integrally connected with the head 101, ahollow stern portion 165 having a shoulder 106 formed thereon forengagement with the end of the sleeve 9d and limiting the movementthereof in one direction. A helical compression spring 107 ofpredetermined spring rate is provided surrounding the stern portion y165land by its engagement with the sleeve Quand the inner end of the head16'1 normally urges the piston 1(10 towards the left, as seen in FIG. 2dependent upon the pressure applied on the outer end thereof throughVthe fluid connection 32.

For one particular set of operating condi-tions, the spring 107 requiresa -force in opposition thereto of the order of 50 p.s.i. before anymovement of the piston 100 occurs.

VThe stern portion of the piston 100 -is provided on the exteriorthereof with a groove 108 for the reception of a packing ring 169, suchas an O-ring, for preventing fluid leakage along the bore 91, the groovelil-8 being longitudinally positioned on the stem portion 1%5 so as toalways be in engagement with the bore 91 iu the Sleeve 9@ upon movomlt Qim@ PSO'n 109( The valve stem portion 105 has an interior longitudinalaxial bore 110 which is provided with vent openings 111 in continuouscommunication therewith and with the vent openings 61 in the housingsection 65.

The bore 110 within the 4interior of the stem portion 105 also serves esa guide for a valve plug 112 which has a plurality of spaced ribs 113thereon for permitting the flow of fluid therealong while guiding thevalve plug 112. The end of the valve stem portion 105 opposite thepiston head 101 lis preferably provided with a frustoconical or taperedportion 114 at the end thereof to serve as a valve seat and the valveplug 112 has a portion 115 for engagement therewith in seat-ingrelation. For purposes of explanation the separable and interengagingvalve plug portion 115 and seat portion 114 will be referred to as valvepart A.

'Ihe valve plug 1.12 also has a cylindrical portion 116 provided with aplurality of ribs 117, guided Within the interior ci the bore 94 forpermitting 4the ilow of fluid therealong.

The valve plug 112 yhas an outwardly extending iiange 118 provided witha plurality of opening 119 therethrough for fluid ilow, the iiange 118being adapted to engage the shoulder 83 for limiting the movement of thevalve plug 112 towards the right, as seen in FIG. 2.

The valve plug 112 is provided with a valve seating portion 120 forengagement with a valve seat 121 at the outer end ofthe sleeve 93. Forpurposes of explanation the separable and interengaging valve seatingportion 120 and valve seat 121 will be referred to as valve part B.

The valve plug 112 is further provided with a bore 130 for the receptionof -a cylindrical stem 13-1 of a check valve plug 132 which has a valvehead 133 of greater diameter for engagement with the valve seat 134formed at the end of 'the bore 130. For purposes off explanation theseparable and interengaging valve head 133 and valve seat 1134 will bereferred to as valve part C.

A compression spring 135 of predetermined spring rate and of -a springrate less than that of the spring 107 is provided surrounding theintermediate portion of the check valve plug 132, and -by its engagementwith the valve head 133 and the flange 118 tends to urge the check valveplug 132 to a posi-tion to close the valve part C, while also urging thehead 118 to a position to close the valve part B.

The check valve plug 132 also has a guide extending therefrom whichincludes a cylindrical portion 136 with a plurality of spaced ribs 137therealong for engagement with the bore 82 to guide the check valve plug132 but to permit uid -flow in open position of the valve part C.

The valve 34, shown in FIG. 3, is substantially the same as thatillustrated and previously described with respect to the valve 31 exceptthat the lboss 57 has the fluid connect-ion 33 connected thereto, theboss 69 has the fiuid connection 36 connected thereto, and the boss S5has the iiuid connection 35 connected thereto, and the check valve plug122 and its associated structure are omitted so that the trailer brakescan be released, as hereinafter explained.

Before tak-ing up the mode of operation of the system illustrated inFIG. 1, ya brief reference will be made to the operation of the valves31 and 34.

The valve 31, as illustrated in FIG. 2 is capable of providing a numberof operating positions. When no pressure is eiective through the iluidconnection 32 and against the head 101 of the piston 100, the pistonhead 101 is urged by the spring 107 'to a position to open the valvepart A so that the iiuid connection y46 is vented to the atmospherethrough the interior vof the bore 110, the vent ports 111 and the ventopenings 61. The valve part B will be closed and the valve part C willbe closed.

As previously indicated, for one particular and preferred character ofoperation, the spring 107 exerts a force in opposition to the fluidpressure applied through the uid connection 32 of the order of 50 p.s.i.before any movement of the 'piston 100 occurs.

When the pressure rises above the predetermined set level, the piston'head 101 moves against the force of the spring 107 to close the valvepart A, thus discontinuing any venting. As the pressure eifectivethrough the fluid connection 32 continues to rise and when it attains avalue of the order of 65 p.s.i., the further movement of the vpistonhead 101 and the stern portion 105 is effective for moving the valveplug 112 to a position to open the valve part B so that communication isestablished between the fluid connections 30 and 46 subject to thecontrol of the check valve plug 132. The valve part B is normally closedby the action of the spring 135 and will remain in closed position untilmoved therefrom by movement of the piston after the Valve part A hasbeen closed. So long as there is no pressure in the fluid connection 30the valve part C will also be closed.

The valve part C is eifective at all times to prevent any flow from theiluid connection 46 to the uid connection 30.

The valve 34 is utilized, as hereinafter explained, for causing abuilding up of etective brake pressure for tractor brake operation ofthe order of 65 p.s.i. before any charging of the trailer brake systemcan occur.

It will be noted that with the valve part B of the valve 34 open theiiuid connection 46 and the bore 81 are connected, and upon a reductionof the pressure effective on the piston head 101 and permitting thepiston 100 to retract, the Valve part B will iirst be closed, and uponfurther retraction of the piston 100 the valve A will be opened forventing the portion of the bore 63 in communication with the iiuidconnection v46.

The friction attendant upon engagement of the packing 103 and thepacking 109 will be such that the actual opening or venting through thevent ports 111 and the vent opening 61 will occur at about 45 p.s.i.

The operation of the valve 34 is suhstantily similar to that previouslyexplained with respect to the valve 31.

The mode of operation will now be described.

Assuming first that there is no pressure in the system, that thecompressor 10 is operated to supply the pressure uid to the wet air tank11 and therefrom to the dry air tank 14, then air under pressure isdelivered through the fluid connection 17 and the branch connection 21and through the dash valve 24 to the uid connection 32 where it isapplied at the valve 31 and to the fluid connection 33 where it isapplied at the valve 34 to position the pistons 100 of the valves 31 and34 as previously explained.

As the pressure in the tank 14 reaches a predetermined value, of theorder of 50 p.s.i., this pressure is eifective against the piston 100 ofthe Valve 31 to initiate movement of the 'piston 100 against the forceof the spring 107 to close the valve part A and cut oit venting of thefluid connection 46. Futher increase in pressure to a level of the orderof 65 p.s.i. and further movement of the piston 100 is eifective foropening the valve part B. Fluid under pressure is thus permitted to flowfrom the tank 14 through the fluid connection 30, past the valve part Cwhich opens to permit the delivery and past the valve part B to theiluid connection 46. The iiuid under pressure delivered to and throughthe iiuid connection 46 is delivered through the emergency relay valve41 for charging the tank 42.

At the same time that the pressure is effective on the valve 31 it isalso eiective at the valve 34 and by movement of its piston 100 alsoiirst cuts off communication of the fluid connection 36 with theatmosphere and then establishes communication between the fluidconnection 35' and the fluid connection 36.

With the tanks 11, 14 and 42 charged with uid under pressure, aspreviously explained, the system is in condition for normal brakeapplying and releasing operation.

If it is desired to partially or wholly apply both the tractor andtrailer brakes, upon operation of the foot valve 22, air under pressure,determined by the movement of the foot valve 22, will be suppliedthrough the uid connection 21 through the uid connection 25 and quickrelease -valve 26 to the brake operating diaphragms 27 of the tractorbrakes. Air will also be supplied through the uid connection 28', thedouble acting check valve 29 and the uid connection 3S, to. and throughthe open valve part B of the tractor protective valve 34 to the serviceline, including the fluid connection 36, the connecting nipple 37, theeXible uid connection 38, the trailer coupling 39,v and to the emergencyrelay valve 41 for applying pressure at the diaphragms 45 of the trailerbrake operating mechanism. The release of the brakes is controlled bythe foot valve 22.

If it is desired to partially or wholly apply the trailer brakes, uponoperation of the hand valve 23, air under pressure determined by themovement of the hand valve 23 will be supplied through the uidconnection 28a, .the

double acting check valve 29, the uid connection 35,V

the tractor protective valve 34 and the service line including the fluidconnection 36, the connecting nipple 37, the tiexible fluid connection38 andthe trailer coupling 39 to the emergency relay valve 41 forapplying pressure at the diaphragms 45 of the trailer brake operatingmechanism. The trailer brakes can berreleased by venting the uidconnection 36 by the hand valve 23.

If it is desired to employ the dash valve 24 for emergency applicationof the trailer brakes, this valve 24 is moved to its emergency positionto quickly vent the uid connection 32. When the fluid connection 32 isvented the valve 31, by the relief of the pressure on its piston 100 isactuated to open the valve part A thereof to vent the fluid connection46 through vent ports 111 and the venting openings 61. The removal ofthe pressure theretofore available at the emergency relay 41 through thefluid connection 46 causes immediate application of the trailer brakesby the pressure available in the tank 42.

The trailer brakes will be released upon reestablishment of the pressurein the huid connection 32.

It will thus be seen that theV system is available for conventionaloperation of both the tractor and trailer brakes, or the trailer brakesalone, or for emergency application of the trailer brakes.

The present invention is particularly suited for conditions over andbeyond those encountered in normal operation. In the event of abreakaway of the trailer from the tractor, it will be noted that thisinvolves a break in the emergency line of the relay valve 41 and in themain service line to the relay valve 41, which for purposes ofexplanation can be considered as a separation of each of the couplings39 and 49.

'lt is essential, upon breakaway of the trailer, thatV tractor brakingbe available and therefore waste of the tractor air must be avoided.

When the pressure in the tanks 11 and 14 yfalls to a predeterminedpressure level, of the order of about 45 p.s.i., the reduction of thepressure on the piston 100 within the valve 3-1 is effective for closingthe valve part B and thus closing off communication between the uidconnection Si? and the uid connection 46, and connecting the fluidconnection 46 through the open valve part A to the vent ports 111 landventing openings 61. No air will be permitted to escape from the tanks11 and 14 at the valve 31 since the uid connection 45 is sealed oi byclosing of the valve part B.

In a similar fashion, the piston 100 of the valve 34 is also retractedby its spring 107 to close off communication between the iluidconnections 36 and 35 by closing of valve part B of the valve 34, sothat no waste of air can occur at this location.

The tractor brakes can then be controlled by the foot valve 22 in themanner previously explained, and with the lowered air pressure.

LIt should be noted that if the emergency line breaks, such as byseparation of the coupling 49, the trailer brakes will be set in themanner previously explained in connection with the operation of the dashvalve 24, and will remain in set condition utilizing the air in thetractor tank 42 until this is lost by leakage.

The protective valves 31 and 34 are useful either with the older type ofleakback valve employed for the emergency relay valve 41 or with the nobleed back type valve employed as valve 41. On the no-bleed back typerelay valves now `available on the market dirt in the system frequentlyfinds its way onto a valve seat so that the no-bleed feature is renderedineffective. The eiect of the undesired leakage is obviated with theprotective valves of the present invention.

If a leak should occur in the tractor system so that the pressure in thetanks 1-1 yand 14 drops, the valve 31 with only the reduced pressureeffective thereagainst would cause venting of the fluid connection 46.When the pressure was reduced to a level of the order of 40 p.s.i thetrailer brakes would beset by the action of the emergency relay 41 inthe manner previously explained.

Under these conditionsrthe only manner in which the trailer brakes couldbe released would be to bleed the trailer tank 42, or upon repair of thetractor leak upon recharging to pressure levels of the order of 65p.s.i. and above, the tank 42 would be recharged and permit the trailerbrake release;

yI claim: Y

l. A protective valve for interposition in the duid lines between thetractor and trailer brake components of tractor trailer type automotivebrake systems and for isolating the tractor brake system upon rupture ofthe fluid lines comprising a housing having a plurality oflongitudinally axially aligned housing sections with separab-le threadedconnections therebetween, a tirst of said A housing sections having ailuid connection for the delivery of a controlling pressure fluidthereinto, a second of said housing sections having a fluid deliveryconnection communicating with the interior thereof, a third of saidhousing sections having a supply fluid connection in communication withthe interior thereof for pressure fluid supply thereto, a piston in saidrst housing section against which said controlling pressure iluid isapplied, a resilient member urging said piston in opposition to theforce of said controlling pressure uid, said piston having a valve sternextending longitudinally axially therefrom in Ysaid housing and fromsaid rst housing section into said second housing section, said valvestem having a passageway therein, said passageway having ventingopenings and said rst housing section having vent ports in communicationwith ythe atmosphere and with which said venting openings are incommunication, a valve member disposed in said second and third housingsections longitudinally axially movable with respect to said stem, saidvalve member and said stem having interengaging portions for cuttingott` communication between the interior of said second housing sectionand said passageway, said valve member having a portion engageable withan interior part of said housing Vfor cutting oi communication betweenthe interior of said third housing section and the interior of saidsecond housing section, the interengaging portions of said stem and saidvalve member in engaged position impelling said valve member to openposition upon predetermined movement of said piston, said piston beingmovable to a plurality of positions including la position in which saidfluid delivery connection is in communication through said ventingopenings and said vent ports with the atmosphere, a position in whichsaid stem and said valve member are engaged |and said vent ports are cutoff, and a position in which with said vent ports cut off communicationis established between the interior of as defined in claim l, inwhich asecond resilient member is provided in said third housing section, and acheck valve is provided in said third housing section with which saidsecond resilient member is in engagement, said check valve beingnormally urged by said second resilient member to cut olf uid ow to saidfluid supply connection.

3. A protective Valve for interposition in the uid lines between thetractor and trailer brake components of tractor trailer type automotivebrake systems and for isolating the tractor brake system upon rupture ofthe tluid lines comprising a housing having a plurality oflongitudinally axially aligned housing sections with separable threadedconnections therebetween, a first of said housing sections having afluid connection for the delivery of a controlling pressure uidthereinto, a second of said housing sections having a uid deliveryconnection communicating with the interior thereof, a third of saidhousing sections havng a supply fluid connection in communication withthe interior thereof for pressure iluid supply thereto, a first hollowsleeve in said second housing section and held in position by theengagement therewith of said first and second housing sections, a secondhollow sleeve in said second housing section and held in position by theengagement therewith of said second and third housing sections, `apiston in said first housing section against which said controllingpressure iiuid is applied. a resilient member urging said piston inopposition to the force of said controlling pressure fluid, said pistonhaving a valve stem extending from said rst housing section into saidsecond housing section in slidable engagement in said r'irst hollowsleeve, said valve stem having a bore therein, said bore having ventingopenings and said rst housing section having vent ports in communicationwith the atmosphere with which said Venting openings are incommunication, a valve member disposed in said second and third housingsections longitudinally axially with respect to said stem, said valvemember having a portion in slidable engagement in said second hollowsleeve, said valve member and said stem having interengaglng portionsfor cutting off communication between the interior of said secondhousing section and said bore, said valve member having a portionengageable with said second sleeve for cutting ott communication betweenthe interior of the third housing section and the interior of the secondhousing section, the interengaging portions of said stem and said valvemember in engaging position impelling said valve member to open positionupon predetermined movement of said piston, said piston being movable toa plurality of positions including a position in which said fluiddelivery connection is in communication through said venting openingsand said vent ports with the atmosphere, a position in which said stemand said valve member `are engaged and said bent ports are cut off, anda position in which with said vent ports cut oi communication isestablished between the interior of said third housing section and theinterior of said second housing section for connecting said uid supplyconnection and said uid delivery connection.

4. A protective valve for automotive brake systems as `defined in claim3, in which a second resilient member is provided in said third housingsection and a check valve is provided in said lthird housing sectionwith which said second resilient member is in engagement, said checkvalve being normally urged by said second resilient mem- -ber to cut olffluid flow to said iluid supply connection.

References .Cited in the le of this patent UNITED STATES PATENTS1,302,538 Gulick May 6, 1919 1,954,662 Bond Apr. 10, 1934 2,331,800Rockwell Oct. 12, 1943 2,361,419 Schnell Oct. 31, 1944 2,404,924Sacchini July 30, 1946 2,470,746 Schultz May 17, 1949 2,579,616Sahlgaard Dec. 25, 1951 2,718,897 Andrews Sept. 27, 1955 2,818,138Ostwald et al Dec. 31, 1957 2,841,178 chultz July 1, 1958 2,859,763Fites Nov. 11, `1958 2,883,997 Schultz Apr. 28, 1959

